E 175 82 (2010)

Designation: E175 − 82 (Reapproved 2010)

Standard Terminology of

Microscopy1

This standard is issued under the fixed designation E175; the number immediately following the designation indicates the year of

original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A

superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

This standard has been approved for use by agencies of the Department of Defense.

Abbe condenser—see condenser, Abbe.

aberration—any error that results in image degradation. Such

errors may be chromatic, spherical, astigmatic, comatic,

distortion, or curvature of field; and can result from design or

execution, or both.

achromatic—literally, color-free. A lens or prism is said to be

achromatic when corrected for two colors. The remaining

color seen in an image formed by such a lens is said to be

secondary chromatic aberration.

achromatic objective—an objective that is corrected chro￾matically for two colors, and spherically for one, usually in

the yellow-green part of the spectrum.

Airy disk—the image of a bright point object, as focused by a

lens system. With monochromatic light, it consists of a

central point of maximum intensity surrounded by alternate

circles of light and darkness caused by the reinforcement and

interference of diffracted rays. The light areas are called

maxima and the dark areas minima. The distribution of light

from the center to the outer areas of the figure was

investigated mathematically by Sir George Airy. The diffrac￾tion disk forms a basis for determining the resolving power

of an ideal lens system. The diameter of the disk depends

largely on the aperture of the lens. The diffraction of light

causing the Airy disk is a factor limiting the resolution of a

well corrected optical system.

analyzer—an optical device, capable of producing plane

polarized light, used for detecting the state of polarization.

a˚ngström unit—a unit of linear measure named after A. J.

Ångström. It is 1 × 10−10 metres; 1 µm = 10,000 Å. It is

generally abbreviated as A. in the United States; elsewhere,

it is variously abbreviated Å , A., A.U., Å., or ÅU.

angular aperture—see aperture, angular.

aperture, angular—the angle between the most divergent rays

that can pass through a lens to form the image of an object.

aperture, effective—the diameter of the entrance pupil; it is

the apparent diameter of the limiting aperture measured from

the front.

aplanatic—corrected for spherical aberration and coma.

apochromatic objective—a lens system whose secondary

chromatic aberrations have been substantially reduced. (See

achromatic).

axis, optical—the line formed by the coinciding principal axes

of a series of optical elements comprising an optical system.

It is the line passing through the centers of curvature of the

optical surfaces.

axis, optic—the direction, or directions in an anisotropic

crystal along which light is not doubly refracted.

balsam, Canada—a resin from the balsam fir Abies balsamea.

Dissolved in xylene, toluene, or benzene it is used as a

mountant for permanent microscopical preparations. Its

refractive index may vary from 1.530 to 1.545 and its

softening point from room temperature to 100°C, these

properties varying with age and solvent content. If impure it

discolors with age.

Bertrand lens—see lens, Bertrand.

bisectrix, acute—in biaxial crystals, that principal axis of the

ellipsoid of indexes which bisects the smaller angle between

the optic axes.

bisectrix, obtuse—in biaxial crystals, that principal axis of the

ellipsoid of indexes which bisects the larger angle between

the optic axes.

calcite—a doubly refracting mineral used in the manufacture

of polarizing prisms. It is uniaxial negative and in the

trigonal diversion of the hexagonal system of crystals. Its

indexes are ´ = 1.486, v = 1.658; its hardness is 3 on the

Mohr scale and specific gravity 2.711.

Canada balsam—see balsam, Canada.

chromatic aberration—a defect in a lens or lens system as a

result of which the lens possesses different focal lengths for

radiation of different wavelengths.

1 This terminology is under the jurisdiction of ASTM Committee E04 on

Metallography and is the direct responsibility of Subcommittee E04.02 on Termi￾nology

Current edition approved July 1, 2010 . Published July 2010. Originally approved

in 1961. Last previous edition approved in 2005 as E175 – 82 (2005). DOI:

10.1520/E0175-82R10.

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